JP2017020445A - Control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device which can suppress the increase of combustion noise to be caused by combustion of pilot injection fuel.SOLUTION: A lower limit pilot injection amount Ql, which is a misfire limit of main injection fuel, is calculated. An upper limit pilot injection amount Qh is calculated so that combustion noise during combustion of pilot injection fuel may fall within an allowable range (ST10). A final pilot injection amount Qf is calculated so as to minimize the amount of smoke to be generated, between the lower limit pilot injection amount Ql and the upper limit injection amount Qh (ST12). Final pilot injection time injf is calculated so as to minimize a difference between a maximum value of an in-cylinder pressure change rate in a combustion period of the pilot injection fuel in executing pilot injection at the final pilot injection amount Qf, and an in-cylinder pressure change rate at the start of the main injection (ST14). Consequently, misfire is prevented, exhaust emission is improved, and combustion noise is reduced.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a control device for an internal combustion engine. In particular, the present invention relates to improved pilot injection control.

  Conventionally, in a diesel engine mounted on a vehicle or the like, pilot injection is executed prior to main injection that contributes to torque generation. That is, the temperature in the combustion chamber is raised by combustion of fuel injected by pilot injection (hereinafter referred to as pilot injected fuel). Thereafter, the fuel injected in the main injection (hereinafter referred to as main injection fuel) is passed through the combustion field of the pilot injection fuel to heat the main injection fuel and suppress the ignition delay of the main injection fuel.

  Patent Document 1 discloses adjusting the injection amount of pilot injected fuel for the purpose of suppressing an increase in combustion noise caused by combustion of pilot injected fuel.

JP 2009-281143 A

  However, there is a limit to suppressing combustion noise only by adjusting the injection amount of the pilot injected fuel. The inventor of the present invention has considered the suppression of combustion noise by optimizing the injection control amount other than the injection amount.

  This invention is made | formed in view of this point, The place made into the objective is providing the control apparatus which can suppress the increase in the combustion sound resulting from combustion of pilot injection fuel.

  The solution of the present invention for achieving the above object is applied to a compression self-ignition internal combustion engine that performs combustion by self-ignition of fuel injected into a cylinder from a fuel injection valve, As a fuel injection, a control device that executes main injection and pilot injection prior to the main injection is assumed. For this control device, an actual gas state quantity calculation unit, an engine operation state quantity detection unit, a compression end temperature estimation unit, a target in-cylinder temperature acquisition unit, a lower limit pilot injection amount calculation unit, an upper limit pilot injection amount calculation unit, and a final pilot injection An amount calculation unit, a final pilot injection timing calculation unit, and a pilot injection command unit are provided. The actual gas state quantity calculation unit calculates the gas quantity, gas composition, gas temperature, and gas pressure in the cylinder. The engine operating state quantity detection unit detects the current rotation speed and load of the internal combustion engine. The compression end temperature estimation unit is configured so that the piston in the cylinder reaches the compression top dead center based on the gas amount, the gas composition, the gas temperature, the gas pressure, the rotation speed, and the load. The compression end temperature resulting from intake air compression is estimated. The target in-cylinder temperature acquisition unit acquires a target in-cylinder temperature at the start of the main injection. The lower limit pilot injection amount calculation unit calculates a lower limit pilot injection amount based on the compression end temperature, the target in-cylinder temperature, the gas amount, and the gas composition. The upper limit pilot injection amount calculation unit calculates an upper limit pilot injection amount based on the rate of change of in-cylinder pressure due to intake air compression, the start timing of the main injection, the gas amount, and the gas composition. The final pilot injection amount calculation unit calculates a pilot injection amount that is a pilot injection amount between the lower limit pilot injection amount and the upper limit pilot injection amount and that minimizes the smoke generation amount as the final pilot injection amount. The final pilot injection timing calculation unit calculates the maximum value of the in-cylinder pressure change rate during the combustion period of the pilot injected fuel and the in-cylinder at the start of the main injection when the pilot injection is executed with the final pilot injection amount. The pilot injection timing that minimizes the deviation from the pressure change rate is calculated as the final pilot injection timing. The pilot injection command unit causes the pilot injection from the fuel injection valve to be executed at the calculated final pilot injection timing.

  With this specific matter, while obtaining the pilot injection amount that minimizes the amount of smoke generated, the maximum value of the in-cylinder pressure change rate during the combustion period of pilot injected fuel and the in-cylinder pressure change rate at the start of main injection By executing the pilot injection at the pilot injection timing at which the deviation is minimized, it is possible to suppress an increase in combustion noise resulting from the combustion of the pilot injected fuel.

  In the present invention, the pilot injection timing at which the deviation between the maximum value of the in-cylinder pressure change rate during the combustion period of the pilot-injected fuel and the in-cylinder pressure change rate at the start of main injection is minimized is calculated as the final pilot injection timing. The pilot injection is executed at this final pilot injection timing. Thereby, the increase in the combustion sound resulting from combustion of pilot injection fuel can be suppressed.

It is a schematic block diagram of the diesel engine which concerns on embodiment, and its control system. It is sectional drawing which shows the combustion chamber of a diesel engine, and its peripheral part. It is a block diagram which shows the structure of control systems, such as ECU. It is a flowchart figure which shows the first half of the procedure of pilot injection control. It is a flowchart figure which shows the second half of the procedure of pilot injection control. It is a figure which shows an example of the cylinder pressure change rate waveform for demonstrating an upper limit pilot injection amount. It is a figure which shows an example of the fuel injection rate waveform for demonstrating an upper limit pilot injection amount. It is a figure which shows an example of the relationship between pilot injection quantity and the amount of smoke generation. It is a figure which shows an example of the fuel injection rate waveform for demonstrating a request | requirement pilot injection time. It is a figure which shows an example of the cylinder pressure change rate waveform for demonstrating request | requirement pilot injection timing.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this embodiment, a case where the present invention is applied to a common rail in-cylinder direct injection multi-cylinder (for example, in-line 4-cylinder) diesel engine (compression self-ignition internal combustion engine) mounted on an automobile will be described.

-Engine configuration-
FIG. 1 is a schematic configuration diagram of a diesel engine 1 (hereinafter simply referred to as an engine) and its control system according to the present embodiment.

  As shown in FIG. 1, the engine 1 according to this embodiment includes a fuel supply system 2, a combustion chamber 3, an intake system 6, and an exhaust system 7.

  The fuel supply system 2 includes a supply pump 21, a common rail 22, an injector (fuel injection valve) 23, an engine fuel passage 24, and the like.

  The supply pump 21 supplies the fuel pumped up from the fuel tank to the common rail 22 through the engine fuel passage 24 after making the pressure high. The common rail 22 distributes high-pressure fuel to the injectors 23. The injector 23 is a piezo injector.

  The intake system 6 includes an intake manifold 61 connected to an intake port 15 a formed in a cylinder head 15 (see FIG. 2), and an intake pipe 62 is connected to the intake manifold 61. In this intake pipe 62, an air cleaner 63, an air flow meter 43, an intercooler 65, and an intake throttle valve (diesel throttle) 64 are arranged in this order from the upstream side.

  The exhaust system 7 includes an exhaust manifold 71 connected to an exhaust port 15 b formed in the cylinder head 15, and an exhaust pipe 72 is connected to the exhaust manifold 71. The exhaust pipe 72 is provided with an NSR (NOx Storage Reduction) catalyst 74 and a DPF (Diesel Particulate Filter) 75.

  As shown in FIG. 2, the cylinder block 11 is formed with a cylinder bore 12 for each cylinder (four cylinders). A piston 13 is accommodated in each cylinder bore 12. A cavity 13 b is recessed in the center of the top surface 13 a of the piston 13, and this cavity 13 b constitutes the combustion chamber 3. The fuel injected from the central portion of the combustion chamber 3 by the injector 23 burns by self-ignition, and the combustion pressure acts on the piston 13. The piston 13 is connected to a crankshaft (not shown) by a connecting rod 18, and engine power is taken out from the crankshaft.

  The cylinder head 15 is provided with an intake valve 16 that opens and closes an intake port 15a and an exhaust valve 17 that opens and closes an exhaust port 15b.

  Further, as shown in FIG. 1, the engine 1 is provided with a turbocharger (supercharger) 5. The turbocharger 5 includes a turbine wheel 52 and a compressor wheel 53 that are connected via a turbine shaft 51.

  Further, the engine 1 is provided with an EGR (Exhaust Gas Recirculation) passage 8 that connects the intake system 6 and the exhaust system 7. The EGR passage 8 is provided with an EGR valve 81 and an EGR cooler 82.

-ECU-
The ECU (Electronic Control Unit) 100 includes a microcomputer (not shown) such as a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and an input / output circuit. As shown in FIG. 3, the input circuit of the ECU 100 includes a crank position sensor 40, a rail pressure sensor 41, a throttle opening sensor 42, an air flow meter 43, exhaust temperature sensors 45a and 45b, a water temperature sensor 46, and an accelerator opening sensor 47. An intake pressure sensor 48, an intake air temperature sensor 49, an in-cylinder pressure sensor 4A, an air-fuel ratio sensor 4B, and the like are connected. Since the functions of these sensors are well known, description thereof is omitted here.

  On the other hand, the supply pump 21, the injector 23, the intake throttle valve 64, the EGR valve 81, and the like are connected to the output circuit of the ECU 100.

  The ECU 100 executes various controls of the engine 1 based on outputs from the respective sensors, calculated values obtained by calculation formulas using the output values, or various maps stored in the ROM. For example, the ECU 100 executes fuel injection control such as pilot injection and main injection as fuel injection control of the injector 23.

  Pilot injection is an operation for injecting a small amount of fuel prior to main injection. This pilot injection has a preheating function for increasing the in-cylinder temperature. That is, the temperature in the cylinder is sufficiently increased until the main injection is started, thereby suppressing the ignition delay of the main injected fuel and ensuring the ignitability of the main injected fuel.

  In the pilot injection control according to the present embodiment, the lower limit pilot injection amount that becomes the misfire limit (misfire limit of the main injected fuel) and the upper limit that becomes the allowable limit of the combustion noise (combustion noise caused by the combustion of the pilot injected fuel). A pilot injection amount that is between the pilot injection amount and that minimizes the amount of smoke generated is obtained. Also, a pilot injection timing that minimizes the drop in the rate of change in pressure in the cylinder during the combustion period of the pilot injected fuel (and thereby minimizes combustion noise) is determined. The pilot injection from the injector 23 is executed at the determined pilot injection timing. The operation of determining the pilot injection timing will be described later.

  The main injection is a fuel injection operation for generating torque of the engine 1. The fuel injection amount and the fuel injection timing in the main injection are determined so as to obtain the required torque according to the operation state quantity such as the engine speed and the accelerator operation amount (engine load). For example, the fuel injection amount is set to be larger as the engine speed is higher and as the accelerator operation amount (accelerator opening) is larger.

  In addition to the pilot injection and main injection described above, after injection and post injection are performed as necessary. Since these injection functions are well known, description thereof is omitted here.

  The fuel injection pressure at the time of executing each fuel injection described above is determined by the internal pressure of the common rail 22 (common rail internal pressure). As the common rail internal pressure, generally, the target rail pressure, which is the target value of the fuel pressure supplied from the common rail 22 to the injector 23, becomes higher as the engine speed increases and the engine load increases. This target rail pressure is set according to a fuel pressure setting map stored in the ROM, for example.

  Further, the ECU 100 controls the opening degree of the EGR valve 81 according to the operating state of the engine 1 and adjusts the exhaust gas recirculation amount (EGR gas amount) toward the intake manifold 61. The amount of EGR gas is set according to an EGR map that is created in advance by experiments, simulations, etc. and stored in the ROM. This EGR map is a map for determining the EGR rate using the engine speed and the engine load as parameters. The ECU 100 controls the opening degree of the EGR valve 81 so as to obtain an EGR gas amount corresponding to the intake air amount so that the EGR rate determined according to the EGR map is established.

-Pilot injection control-
Next, pilot injection control, which is a feature of this embodiment, will be described. In this pilot injection control, as described above, it is a pilot injection amount between the lower limit pilot injection amount that becomes the misfire limit and the upper limit pilot injection amount that becomes the allowable limit of combustion noise, and minimizes the amount of smoke generated. Obtain the pilot injection amount. Further, the pilot injection timing that minimizes the drop in the pressure change rate in the cylinder during the combustion period of the pilot injected fuel is determined. The pilot injection from the injector 23 is executed at the determined pilot injection timing. The outline of this pilot injection control will be described below.

  In this pilot injection control, (a) an operation for calculating the gas amount, gas composition, gas temperature, and gas pressure in the cylinder, and (b) a rotational speed and a load that are current operation state amounts of the engine 1 are detected. (C) Intake compression when the piston in the cylinder reaches the compression top dead center based on the operation, (c) the gas amount, the gas composition, the gas temperature, the gas pressure, the rotational speed, and the load (D) an operation for obtaining a target in-cylinder temperature at the start of main injection, (e) the compression end temperature, the target in-cylinder temperature, the gas amount, and the An operation for calculating a lower limit pilot injection amount based on the gas composition; (f) a rate of change of the in-cylinder pressure due to intake air compression, a main injection start timing, the gas amount, and an upper limit pyrol (G) a pilot injection amount between the lower limit pilot injection amount and the upper limit pilot injection amount, and a pilot injection amount that minimizes the smoke generation amount is calculated as a final pilot injection amount (H) The maximum value of the in-cylinder pressure change rate during the combustion period of the pilot-injected fuel and the in-cylinder pressure change rate at the start of main injection when pilot injection is executed with the final pilot injection amount The operation of calculating the pilot injection timing at which the deviation from the minimum is the final pilot injection timing, and (i) the operation of executing the pilot injection from the injector 23 (fuel injection valve) at the calculated final pilot injection timing is sequentially performed. . Details of the operations (a) to (i) will be described later.

  These operations are executed by the ECU 100. For this reason, in the ECU 100, a functional part that executes the operation (a) is configured as an actual gas state quantity calculation unit referred to in the present invention. In the ECU 100, a functional part that executes the operation (b) is configured as an engine operating state quantity detection unit referred to in the present invention. In the ECU 100, a functional part that executes the operation (c) is configured as a compression end temperature estimation unit in the present invention. In the ECU 100, a functional part that executes the operation (d) is configured as a target in-cylinder temperature acquisition unit referred to in the present invention. In the ECU 100, a functional part that executes the operation (e) is configured as a lower limit pilot injection amount calculation unit in the present invention. The functional part that executes the operation (f) is configured as an upper limit pilot injection amount calculation unit in the present invention. The functional part that executes the operation (g) is configured as a final pilot injection amount calculation unit in the present invention. The functional part that executes the operation (h) is configured as a final pilot injection timing calculation unit in the present invention. The functional part that executes the operation (i) is configured as a pilot injection command unit in the present invention.

  These actual gas state quantity calculation unit, engine operation state quantity detection unit, compression end temperature estimation unit, target in-cylinder temperature acquisition unit, lower limit pilot injection amount calculation unit, upper limit pilot injection amount calculation unit, final pilot injection amount calculation unit, final The pilot injection timing calculation unit and the pilot injection command unit constitute a control device according to the present invention.

  Hereinafter, a specific procedure of this pilot injection control will be described with reference to the flowcharts of FIGS. This flowchart shows after every start of the engine 1 every time the crankshaft rotates by a predetermined angle (more specifically, every time before pilot injection is started in any cylinder; for example, the piston 13 is compressed Every timing at which the predetermined crank angle position is reached before reaching the dead point: Since the engine according to the present embodiment has four cylinders, the ECU 100 is started every 180 ° CA). Hereinafter, a cylinder in which the pilot injection control amount is defined in the pilot injection control (a cylinder that has reached the timing before the pilot injection is started) is referred to as a control target cylinder.

  First, in step ST1, the current state quantity of gas introduced into the cylinder to be controlled is acquired. Specifically, the gas amount gcyl, the gas composition C, the gas temperature T, and the gas pressure P are calculated.

  The gas amount gcyl is the mass of intake air introduced into the cylinder to be controlled, and is obtained based on output signals from the air flow meter 43 and the intake air temperature sensor 49. For example, the intake air amount (the integrated value of the intake air amount calculated based on the output signal from the air flow meter 43) during a predetermined period (for example, during the period from when the intake valve 16 of the cylinder to be controlled is opened to when it is closed) ) And a predetermined arithmetic expression or map using the intake air temperature (the intake air temperature detected by the output signal from the intake air temperature sensor 49) as a parameter, the gas amount gcyl is obtained. The larger the intake air amount and the lower the intake air temperature, the larger the gas amount gcyl is calculated. Further, the gas amount gcyl is calculated by adding the EGR gas amount (EGR gas amount for achieving the EGR rate read from the EGR map) to the gas amount obtained based on the output signal from the air flow meter 43 or the like. You may make it do.

  The gas composition C is the oxygen concentration in the gas introduced into the cylinder to be controlled, and is obtained from the EGR rate, the air-fuel ratio (A / F), and the like. The EGR rate is read from the EGR map as described above. The air-fuel ratio is detected by an output signal from the air-fuel ratio sensor 4B. The gas composition C is obtained from a predetermined arithmetic expression or map using the EGR rate and the air-fuel ratio (A / F) as parameters. The gas composition C (oxygen concentration in the gas) is calculated as a higher value as the EGR rate is lower and as the air-fuel ratio (A / F) is larger.

  The gas temperature T varies depending on the compressed state of the gas as the piston 13 reciprocates. The intake gas sucked into the cylinder to be controlled in the intake stroke (intake gas having the intake temperature detected by the output signal from the intake temperature sensor 49) is the piston 13 in the compression stroke after the intake valve 16 is closed. The compression ratio of the suction gas is determined by the piston position geometrically determined at the present time (when the gas temperature T is calculated), so that the gas temperature T at this time is calculated. Can do. In step ST1, this gas temperature T is acquired.

  The gas pressure P also changes depending on the compressed state of the gas as the piston 13 reciprocates. The intake gas sucked into the cylinder to be controlled in the intake stroke (the intake gas having the intake pressure detected by the output signal from the intake pressure sensor 48) is the piston 13 in the compression stroke after the intake valve 16 is closed. The compression ratio of the suction gas is determined by the piston position geometrically determined at the present time (when the gas pressure P is calculated), so that the gas pressure P at this time is calculated. Can do. In step ST1, this gas pressure P is acquired. The gas pressure P can also be detected by an output signal from the in-cylinder pressure sensor 4A.

  The operation of this step ST1 corresponds to the “operation by the actual gas state quantity calculation unit, which calculates the gas amount, gas composition, gas temperature, and gas pressure in the cylinder” in the present invention.

  In step ST2, the current engine speed Ne and engine load Q (which are values corresponding to the total injection amount of the pilot injection amount and the main injection amount) are detected. The engine speed Ne is calculated based on an output signal (pulse waveform signal) from the crank position sensor 40. The engine load Q is calculated based on the engine speed and the output signal from the accelerator opening sensor 47.

  The operation of step ST2 corresponds to the “operation by the engine operating state quantity detection unit, which detects the current rotational speed and load of the internal combustion engine” in the present invention.

  In step ST3, an in-cylinder temperature (compression end temperature) Tc when the piston 13 reaches the compression top dead center is calculated (estimated). The compression end temperature Tc is obtained from a predetermined arithmetic expression or map using the gas amount gcyl, the gas composition C, the gas temperature T, the gas pressure P, the engine rotational speed Ne, and the engine load Q as parameters. Desired. As the gas amount gcyl increases, the gas composition C (oxygen concentration in the gas) increases, the gas temperature T increases, the gas pressure P increases, the engine rotational speed Ne increases, and the engine load Q increases. The higher the is, the higher the compression end temperature Tc is calculated.

  The operation of this step ST3 is “operation by the compression end temperature estimation unit” in the present invention, and the piston in the cylinder is determined based on the gas amount, gas composition, gas temperature, gas pressure, rotation speed, and load. This corresponds to the operation of estimating the compression end temperature resulting from the intake compression when the compression top dead center is reached.

  In step ST4, the target in-cylinder temperature Tt is acquired. Here, the target in-cylinder temperature Tt at the start of main injection is acquired. An example of the target in-cylinder temperature Tt is a diffusion combustion temperature of fuel (for example, 1000 K). The target in-cylinder temperature Tt is not limited to this. The target in-cylinder temperature Tt is obtained by experiments or the like as a temperature at which the main injected fuel does not misfire and is stored in the ROM in advance. In step ST4, this temperature is acquired.

  The operation in step ST4 corresponds to the “operation by the target in-cylinder temperature acquisition unit that acquires the target in-cylinder temperature at the start of main injection” in the present invention.

  In step ST5, a lower limit pilot injection amount Ql is calculated. The lower limit pilot injection amount Ql is a pilot injection amount that becomes a misfire limit of the main injected fuel. That is, this is the minimum pilot injection amount that is necessary to raise the cylinder temperature to the ignition temperature of the main injected fuel. The lower limit pilot injection amount Ql is obtained from a predetermined arithmetic expression or map using the compression end temperature Tc, the target in-cylinder temperature Tt, the gas amount gcyl, and the gas composition C as parameters. Further, the lower the compression end temperature Tc, the higher the target in-cylinder temperature Tt, the greater the gas amount gcyl, and the lower the gas composition C (oxygen concentration in the gas), the greater the lower limit pilot injection amount Ql. Calculated as a value.

  The operation of this step ST5 is the operation by the “lower limit pilot injection amount calculation unit” in the present invention, and the lower limit pilot injection amount is calculated based on the compression end temperature, the target in-cylinder temperature, the gas amount, and the gas composition. Corresponds to “operation to perform”.

  In step ST6, an in-cylinder volume Vcyl at the start of main injection is acquired. This in-cylinder volume Vcyl is the in-cylinder volume Vcyl at the reference injection timing of main injection (stored in the ROM) assigned to the operation grid point corresponding to the current engine speed and engine load. That is, in step ST6, the cylinder volume Vcyl determined by the position of the piston 13 corresponding to the crank angle position at the start of main injection is read.

  In step ST7, the in-cylinder pressure change rate dP / dθ is calculated. This in-cylinder pressure change rate dP / dθ is the amount of change in the in-cylinder pressure per unit crank angle accompanying the movement of the piston 13 in the cylinder to be controlled. That is, the in-cylinder pressure change rate dP / dθ due to so-called motoring. The in-cylinder pressure change rate dP / dθ is the gas amount gcyl, the gas composition C, the gas temperature T, the gas pressure P, the engine rotational speed Ne, the engine load Q, and the start time of the main injection. It is obtained from a predetermined arithmetic expression or map using the in-cylinder volume Vcyl as a parameter. For example, the larger the gas amount gcyl, the higher the gas composition C (oxygen concentration in the gas), the lower the gas temperature T, the higher the gas pressure P, the higher the engine speed Ne, the higher the engine load Q. As the in-cylinder volume Vcyl at the start of main injection increases, the in-cylinder pressure change rate dP / dθ is calculated as a higher value.

  In step ST8, the main injection start timing (crank angle position) injm is acquired. The main injection start timing injm is a reference injection timing of main injection (stored in the ROM) assigned to the operation grid point corresponding to the current engine speed and engine load.

  In step ST9, the fuel injection amount change rate dQ / dθ is calculated. The fuel injection amount change rate dQ / dθ is a change amount of the fuel injection amount per unit crank angle when pilot injection is executed in the cylinder to be controlled. The fuel injection amount change rate dQ / dθ is obtained from a predetermined arithmetic expression or map using the in-cylinder pressure change rate dP / dθ, the gas composition C, and the in-cylinder volume Vcyl at the start of the main injection as parameters. It is done. For example, the greater the in-cylinder pressure change rate dP / dθ, the higher the gas composition C (oxygen concentration in the gas), and the greater the in-cylinder volume Vcyl at the start of main injection, the greater this fuel injection amount change rate dQ. / Dθ is calculated as a high value.

  In step ST10 (FIG. 5), an upper limit pilot injection amount Qh is calculated. This upper limit pilot injection amount Qh is a pilot injection amount for setting the combustion noise during the combustion of pilot injected fuel within an allowable range. The upper limit pilot injection amount Qh is obtained from a predetermined arithmetic expression or map using the fuel injection amount change rate dQ / dθ, the main injection start timing injm, the gas amount gcyl, and the gas composition C as parameters. For example, the larger the fuel injection amount change rate dQ / dθ, the higher the main injection start timing injm, the greater the gas amount gcyl, and the higher the gas composition C (oxygen concentration in the gas), The upper limit pilot injection amount Qh is calculated as a small value.

  FIG. 6 is a diagram showing an example of the in-cylinder pressure change rate waveform for explaining the upper limit pilot injection amount Qh. Injm in FIG. 6 is the start timing of the main injection. FIG. 7 is a diagram showing an example of a fuel injection rate waveform for explaining the upper limit pilot injection amount Qh.

  The waveform indicated by the solid line in FIG. 6 is a waveform of the in-cylinder pressure change rate dP / dθ that changes as the piston 13 moves in the cylinder to be controlled. That is, it is a waveform of the in-cylinder pressure change rate dP / dθ due to motoring. In step ST10, a region indicated by a broken line in FIG. 6 is calculated as the upper limit pilot injection amount Qh. That is, the pilot injection fuel injected during the period up to the start timing injm of the main injection in a range where the in-cylinder pressure change rate dP / dθ does not exceed the peak value of the in-cylinder pressure change rate dP / dθ due to the motoring. Is defined as the upper limit pilot injection amount Qh. In other words, when the pilot injection is executed with an injection amount larger than the upper limit pilot injection amount Qh, the in-cylinder pressure change rate dP / dθ resulting from the combustion of the pilot injected fuel is the in-cylinder pressure due to motoring. Since the peak value of the rate of change dP / dθ is exceeded and the combustion noise increases, the upper limit pilot injection amount Qh is obtained as the maximum value of the pilot injection amount for suppressing the increase in combustion noise.

  Further, when the pilot injection is executed with the upper limit pilot injection amount Qh, the fuel injection rate waveform as shown in FIG. 7 is obtained. That is, when the fuel injection rate waveform of pilot injection becomes larger than the fuel injection rate waveform shown in FIG. 7 (when the area of the fuel injection rate waveform increases), the combustion noise exceeds the allowable range.

  The operation of step ST10 is an operation by the “upper limit pilot injection amount calculation unit” according to the present invention, and is based on the rate of change of the in-cylinder pressure due to intake air compression, the start timing of main injection, the gas amount, and the gas composition. Corresponds to “the operation for calculating the upper limit pilot injection amount”.

  In step ST11, the rail pressure (fuel injection pressure) pcr is detected. This rail pressure pcr is detected by an output signal from the rail pressure sensor 41.

  In step ST12, a final pilot injection amount Qf is calculated. The final pilot injection amount Qf is a pilot injection amount between the lower limit pilot injection amount Ql and the upper limit pilot injection amount Qh, and is calculated as a pilot injection amount that minimizes the amount of smoke generated. One of the causes of this smoke generation is that the combustion field of the pilot injection fuel and the combustion field of the main injection fuel overlap, and oxygen shortage occurs in this region.

  The final pilot injection amount Qf is obtained from a predetermined arithmetic expression or map using the lower limit pilot injection amount Ql, the upper limit pilot injection amount Qh, the gas amount gcyl, the gas composition C, and the rail pressure pcr as parameters. It is done. For example, as the gas amount gcyl increases, the higher the gas composition C (oxygen concentration in the gas), and the higher the rail pressure pcr, the larger the final pilot injection amount Qf is calculated. When the pilot injection amount calculated by these parameters is a value between the lower limit pilot injection amount Ql and the upper limit pilot injection amount Qh, the calculated pilot injection amount is the final pilot injection amount. Qf. If the calculated pilot injection amount is smaller than the lower limit pilot injection amount Ql, the lower limit pilot injection amount Ql becomes the final pilot injection amount Qf. If the calculated pilot injection amount is larger than the upper limit pilot injection amount Qh, the upper limit pilot injection amount Qh becomes the final pilot injection amount Qf.

  FIG. 8 is a diagram illustrating an example of the relationship between the pilot injection amount and the smoke generation amount. Thus, the smoke generation amount changes according to the pilot injection amount. In the example shown in FIG. 8, a pilot injection amount that can minimize the amount of smoke generated exists between the lower limit pilot injection amount Ql and the upper limit pilot injection amount Qh. In step ST12, a pilot injection amount that can minimize the amount of smoke generated is calculated as a final pilot injection amount Qf.

  The operation of this step ST12 is an operation by the final pilot injection amount calculation unit referred to in the present invention, which is a pilot injection amount between the lower limit pilot injection amount and the upper limit pilot injection amount, and minimizes the smoke generation amount. This corresponds to “operation for calculating the pilot injection amount to be performed as the final pilot injection amount”.

  In step ST13, the required in-cylinder pressure change rate is calculated. This required in-cylinder pressure change rate is the maximum value of the in-cylinder pressure change rate for keeping the combustion noise during the combustion of the pilot injected fuel within an allowable range. The required in-cylinder pressure change rate is a predetermined value in which the deviation between the maximum value of the in-cylinder pressure change rate during the combustion period of the pilot injected fuel and the in-cylinder pressure change rate at the start of main injection is set in advance. The value is within the value. That is, when this deviation exceeds a predetermined value, the combustion noise during the combustion of the pilot injected fuel exceeds the allowable range. Therefore, the required in-cylinder pressure change rate is obtained as a value in which the deviation does not exceed the predetermined value. This required in-cylinder pressure change rate may be obtained by an experiment or the like and stored in advance in the ROM, or may be calculated according to the current engine speed and engine load. .

  In step ST14, the final pilot injection timing injf is calculated. The final pilot injection timing injf includes the maximum value of the in-cylinder pressure change rate dP / dθ during the combustion period of the pilot injected fuel and the start of the main injection when pilot injection is executed with the final pilot injection amount Qf. This is the pilot injection timing at which the deviation from the in-cylinder pressure change rate dP / dθ at the time is minimized.

  The final pilot injection timing injf is obtained from a predetermined arithmetic expression or map using the required in-cylinder pressure change rate, the gas amount gcyl, the gas composition C, the gas temperature T, and the gas pressure P as parameters. .

  FIG. 9 is a diagram showing an example of a fuel injection rate waveform for explaining the required pilot injection timing. FIG. 10 is a diagram showing an example of the in-cylinder pressure change rate waveform for explaining the required pilot injection timing. In these drawings, the fuel injection rate waveform and the in-cylinder pressure change rate waveform in three pilot injections having the same pilot injection amount (final pilot injection amount Qf) and different pilot injection timings are shown. 10 is a waveform of the in-cylinder pressure change rate dP / dθ that changes with the movement of the piston 13 (a waveform of the in-cylinder pressure change rate dP / dθ due to motoring). Further, the waveform indicated by the bold solid line in FIG. 10 is the waveform of the in-cylinder pressure change rate dP / dθ resulting from the combustion of fuel.

  Of the injection rate waveform and in-cylinder pressure change rate waveform of the pilot injected fuel in these figures, the waveform indicated by the solid line (see waveform P1 in FIGS. 9 and 10) is another waveform (the waveform indicated by the broken line; waveform P2 , P3), the deviation between the maximum value of the in-cylinder pressure change rate dP / dθ during the combustion period of the pilot injected fuel and the in-cylinder pressure change rate dP / dθ at the main injection start time injm is small. (See deviation ΔdP / dθ in FIG. 10). In this way, the deviation ΔdP / dθ between the maximum value of the in-cylinder pressure change rate dP / dθ during the combustion period of the pilot-injected fuel and the in-cylinder pressure change rate dP / dθ at the start time injm of the main injection is reduced. Thus, combustion noise can be reduced. In step ST14, the pilot injection timing that can minimize the combustion noise is calculated as the final pilot injection timing injf.

  The operation of this step ST14 is the “operation by the final pilot injection timing calculation unit” in the present invention, and when the pilot injection is executed with the final pilot injection amount, the in-cylinder pressure change during the combustion period of this pilot injected fuel This corresponds to an operation of calculating the pilot injection timing at which the deviation between the maximum value of the rate and the in-cylinder pressure change rate at the start of the main injection is minimum as the final pilot injection timing.

  In step ST15, it is determined whether or not the pilot injection execution timing (final pilot injection timing injf) has come (the crank angle position has reached the final pilot injection timing injf).

  If the pilot injection execution timing has not yet been reached, a NO determination is made in step ST15 to wait until this execution timing is reached.

  When the execution timing of pilot injection is reached and YES is determined in step ST15, the process proceeds to step ST16, and pilot injection is executed.

  The operation of step ST16 corresponds to the “operation by the pilot injection command unit, which executes pilot injection from the fuel injection valve at the calculated final pilot injection timing” in the present invention.

  The above operation is repeated every time the crankshaft rotates by a predetermined angle (every time before pilot injection is started in any cylinder).

  Since such pilot injection control is performed, the control device for the internal combustion engine according to the present invention is configured by the ECU 100 (more specifically, by each functional portion in the ECU 100 described above). The control device includes signals from the crank position sensor 40, rail pressure sensor 41, air flow meter 43, accelerator opening sensor 47, intake pressure sensor 48, intake air temperature sensor 49, in-cylinder pressure sensor 4A, air-fuel ratio sensor 4B, and the like. Is received as an input signal. In addition, this control device is configured to output a pilot injection command signal as an output signal to each injector 23.

  As described above, in the present embodiment, the final pilot injection amount Qf that is the pilot injection amount between the lower limit pilot injection amount Ql and the upper limit pilot injection amount Qh and that minimizes the smoke generation amount is calculated. Yes. The final pilot in which the deviation ΔdP / dθ between the maximum value of the in-cylinder pressure change rate dP / dθ during the combustion period of the pilot-injected fuel and the in-cylinder pressure change rate dP / dθ at the start time injm of the main injection is minimized. The injection timing injf is calculated. The pilot injection is executed at the final pilot injection amount Qf and the final pilot injection timing injf. Thereby, it is possible to prevent misfire, improve exhaust emission, and reduce combustion noise.

  In the present embodiment, the control amount of pilot injection is determined by feedforward control. For this reason, generation | occurrence | production of misfire, deterioration of exhaust emission, and increase of a combustion sound can be prevented beforehand.

-Other embodiments-
In the embodiment described above, the case where the present invention is applied to the in-line four-cylinder diesel engine 1 mounted on an automobile has been described. The present invention is applicable not only to automobiles but also to engines used for other purposes. Further, the number of cylinders and the engine type (separate type engine, V-type engine, horizontally opposed engine, etc.) are not particularly limited.

  Moreover, although the said embodiment demonstrated the case where this invention was applied to the engine 1 of a conventional vehicle (vehicle which mounted only an engine as a driving force source), the vehicle which mounts an engine and an electric motor as a driving force source. The present invention can also be applied to the engine.

  The present invention is applicable to pilot injection control in a diesel engine mounted on an automobile.

1 engine (internal combustion engine)
3 Combustion chamber 23 Injector (fuel injection valve)
100 ECU

Claims (1)

Applied to a compression self-ignition internal combustion engine that performs combustion by self-ignition of fuel injected into a cylinder from a fuel injection valve. As fuel injection from the fuel injection valve, main injection and pilot injection preceding this main injection In a control device that executes
An actual gas state amount calculating section for calculating the gas amount, gas composition, gas temperature, and gas pressure in the cylinder;
An engine operating state detection unit for detecting the current rotational speed and load of the internal combustion engine;
Based on the gas amount, the gas composition, the gas temperature, the gas pressure, the rotational speed, and the load, the compression end resulting from the intake compression when the piston in the cylinder reaches the compression top dead center A compression end temperature estimator for estimating the temperature;
A target in-cylinder temperature acquisition unit for acquiring a target in-cylinder temperature at the start of the main injection;
A lower limit pilot injection amount calculation unit that calculates a lower limit pilot injection amount based on the compression end temperature, the target in-cylinder temperature, the gas amount, and the gas composition;
An upper limit pilot injection amount calculation unit that calculates an upper limit pilot injection amount based on the rate of change of in-cylinder pressure due to intake compression, the start timing of the main injection, the gas amount, and the gas composition;
A final pilot injection amount calculation unit that calculates a pilot injection amount between the lower limit pilot injection amount and the upper limit pilot injection amount and that minimizes the smoke generation amount as a final pilot injection amount;
When pilot injection is executed with the final pilot injection amount, the deviation between the maximum value of the in-cylinder pressure change rate during the combustion period of the pilot-injected fuel and the in-cylinder pressure change rate at the start of the main injection is minimal. A final pilot injection timing calculation unit that calculates the pilot injection timing as the final pilot injection timing,
A pilot injection command section for executing the pilot injection from the fuel injection valve at the calculated final pilot injection timing;
A control device for an internal combustion engine, comprising:

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